How to change the COM port for a USB Serial adapter on Windows 7, 8, 8.1, and 10

Start by going to the Device Manager. Once there do the following:
Expand the Ports ‘(COM& LPT)’

You should be looking at something like this:

As you can see Windows has set the port to COM10. However many legacy applications expect the port to be between 1-4. Let’s change that:
Right click on the device and click on ‘Properties’.

Click on ‘Port Settings’. Then click on ‘Advanced…’.

Once you’re in ‘Advanced Settings for COM10’ on the bottom you can see the ‘COM Port Number: COM10’. Click on that to change it to the lowest possible number (between 1-4).

Then click ‘OK’ on all open Property Windows.
Now the device should look like this:

97 comments on “How to change the COM port for a USB Serial adapter on Windows 7, 8, 8.1, and 10”

  1. Philmore Sydney Reply

    Just what to say thanks. This website has been very useful in assisting me in getting my usb to serial adapter to work. On my computer however there are no serial ports but when I follow the steps as above to change the com port when the usb to serial is plugged in quite a few of the ports in the drop down list has the status ‘in use’ next to them. Can you tell me the reason for this?


      • laserman Reply

        I found a code that allows you to remove old associations to COM Ports. You can then plug your adapter in and then associate it with the COM Port you need.

        1. Start, All Programs, Accessories, Right-click “Command Prompt” in Accessories and choose “Run as Administrator”
        2. Enter “set devmgr_show_nonpresent_devices=1″ – without the quotes obviously
        3. Enter “start devmgmt.msc”
        4. In the box that opens, select “Show hidden devices” in the ‘view’ menu.

        Now if you expand the section on COM ports, all the COM ports that have ever
        been created will be displayed, the non present ones being in grey. You can
        uninstall away anything that you don’t want (right click, select uninstall).

        • Richard Z Reply

          THANK YOU! I’ve tried 3 devices and about 5 hours trying to download track data from a Garmin GPSMap 76 onto a windows 8 PC using a USB to Serial adaptor. Nothing worked, I was just about to give up when I found your guidance to clear out the old com ports. That did the trick, and the Plugable USB-Serial adaptor finally worked. You saved a PC from taking a short trip across the room in frustration!

        • Jim T Reply

          Perfect tool! I needed to clear out the com associations for some serial
          adaptors I had repaired. Thanks!

        • computer user Reply

          I almost gave up on getting my arduino nano to upload. This saved me. It seems to only like com6 for some reason. and that was taken, Thank you… you advice still going after 8 years.

          • Pat


            You’re very welcome! I am glad to hear that our serial adapter documentation can still be helpful to you! Have a great day!

            Plugable Technology

      • Ronny Reply

        To remove all com port associations open notepad and paste following code

        Windows Registry Editor Version 5.00

        [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\COM Name Arbiter]

        and save as all files

        Reset Com Ports In Use.reg

        Then Run ‘Reset Com Ports In Use.reg’ file as Administrator.

  2. Canton Reply

    Thanks a lot for the helpful article. If you don’t mind though, I’d appreciate you’re help, as I’m a bit stuck. When I go to the “properties” dialog for my USB to Serial Port, there is no tab for “port settings.” The tab does appear in the properties dialog of other COM ports though, just not the USB to Serial port. I’ve tried updating the driver, to no avail.

    Any help would be much appreciated!

    • Bernie Thompson Reply

      Hi Canton – Can you say what brand of adapter (and if not Plugable, what chipset / driver), and what OS you’re on. Thanks!

  3. matt Reply

    There is no tab for port settings in windows 7 home. Do u know how to change port settings in windows 7 home?

    • Jeff Everett Reply

      Hi Matt-

      Sorry to hear you’re not seeing the port settings tab, and the delay in getting back to you.

      Our screenshots for this article were done on Windows 7 Home, and the user interface is the exact same on Pro and Ultimate just for the record.

      We’re happy to help if you’re still stuck on this and want to provide a little more info: are you seeing the “Prolific USB-Serial Comm Port” device under device manager, or something else?

      Jeff Everett
      MCITP Enterprise Support Tech

  4. Pingback: Installing the Plugable USB to RS-232 DB9 Serial Adapter on Windows 7 | Plugable

  5. ray Reply

    I also have the problem where the Prolific USB to serial is installed on com11 and the “advanced” button leads to anohter screen, but there is no provision for changing com port there. Might be IT department blocks that on company PC. I blame the device driver installation software -it SHOULD show defaults and ASK the user if they want to make changes before installing. No nothings can just push the button to install defaults, those of use who know what settings we need could then get it right.

  6. Brad Fluharty Reply

    I just received my Plugable USB to RS-232 DB9 Serial Adapter, and after downloading and installing the updated drivers and tweaking the Com port, was able to use my Icom PCR-1000 for the first time in 6 or 7 years. Receiver software still telling my that it cannot find the port, but it seems to be fully functional. Brad

  7. Steve Reply

    Is there any way to make sure that Windows 7 does NOT swap the port setting once they are set using the above method?

  8. Pingback: NiTek Q Support

  9. Ganesha.B.S Reply

    How can I open the port in windows 7 and send commands to that port also get acknowledgement?

  10. Gellan Reply

    thank you so much. I wanted to change the port number of my arduino, but couldn’t find a way to do so. this is the one and only method which worked for me. thanks again for sharing.

  11. Gerry Reply

    none of that worked for me . I am trying to down load a game & it keeps giving me errors when I try to change the port there is nothing there.

  12. Pingback: Com port problem with tk-8180 - The Forums

  13. Ian Millard Reply

    Suppose You’re using a modern computer, and there is no device entry for Ports (COM & LPT) because the computer only has USB Ports.
    Then what?

    • Bernie Thompson Reply

      Thanks for asking. All modern OSes support virtual COM ports. That’s the mechanism the Bluetooth support in Windows and OS X is using.

  14. Sam Ford Reply

    Hi Bernie – I’m not sure if your postings on this topic has closed.

    I had an “Ham” HF radio connected to a desktop XP and a logging program via RS-232. As I changed bands on the radio, the log program would follow, recording time and date and the frequency of operation. Then, the PC was struck by lightning and I got another PC with new motherboard running Windows 7.

    I now have a radio that runs a USB cable that controls a Contest Logging program However when using an RS232 cable to control my normal logging for contacts, the program does not see the radio or the cable.

    I have tried changing the port numbers but the program still does not see the radio. The two existing ports are 1 and 3 both with Nuvoton Drivers. I tried deleting them but then can not create a new COM1. With the drivers back into the PC, I tried using COM3 for the Ham Logging program but there is still no ‘comms’ between the radio and PC.

    Please HELP !!

    • Jeanie Reply

      Hi Sam, Did you ever get this issue fixed? My father is having the same issue with a logging program and an Elecraft K3. Any help would be appreciated!

      • David Roberts Reply

        HI Jeanie and Sam, Thank you for posting. Could you please let me know what device you are connecting to and what the program is that is communicating? It would probably be best to email me directly at Thanks!

      • Sam Ford Reply

        Hi Jeanie

        I’m a complete computer illiterate !! Still not sorted yet. I used to run Swisslog with my TS-2000S using a serial cable. A few months ago, I acquired a TS-590S after selling the TS-2000., I entered a small contest and had N1MM installed using a USB cable. The RS-232 port was used to control the Experk 1K-FA linear. During the contest, N1MM and the linear worked fine.

        After the contest, I tried running SwissLog but the program could not see the COM port. Reading user comments that N1MM and any logging program can not run together, I removed N1MM although they were on different COM ports Now, I keep getting a message that the Com port I am setting up for Swisslog is being used by another device although there are no other devices connected to the PC. I’ve tried changing the Start and Stop bits and tried various combinations and getting more frustrated !

        I trust that your dad will have better luck


  15. Ohnomagicsmoke Reply

    I’ve got a curly one, I’m running PLC’s and simulators through a USB serial converter however every time a new windows session is started some terminals forget their com numbers and I have to reassign them, with close to 100 work stations this is tiresome do you know what the underlying issue is?

    • David Roberts Reply

      Thank you for posting your question. What software are you using on the workstations to connect to the PLC’s and simulators? I’m assuming the COM port itself isn’t changing, just the setting in the terminal software.

  16. Pauline Chang Reply

    I am trying to use two 485 Ports at the same time. It looks like when I open the second port, the first connection seems to be disconnected automatically. Is there any way to open/ use two ports at the same time?

  17. terrence m Reply

    Im getting error 10 device not started when connecting the serial to usb cable. Any advice ?.

  18. Mauricio A Reply

    I am trying to use two COM Ports at the same time. It looks like when I open the second port, the first connection seems to be disconnected automatically. Is there any way to use two ports at the same time?

  19. Ted Reply

    Hi! Thank you very much!
    Question: How can I add a port (com)?! I ‘ve got jut one port (for a printer) or can I change it in order to use it for another apparatus (a sat receiver)?
    Thanks.. Regards

  20. sarathpradeep Reply

    my pc -device manager not showing-any” PORT(COM&LPT)”
    how to get it back.what will be the reason for that.

    • David Roberts Reply

      Thanks for posting! If this isn’t showing in Device Manager, it probably means that the driver for the adapter is not working properly or hasn’t been installed. If you have a Plugable USB – RS-232 adapter, please contact us at and we can help troubleshoot this. Thanks!

  21. Paul Aeberli Reply

    Hi, I am trying to connect a UT61B multimeter to my dell laptop win7 home via a usb to serial cable. They do not specify one.The meter comes with a female 9 pin connector which works fine when connected to an older WXP desktop unit with traditional com ports.. I borrowed a Prolific (green) cable to try it on the Dell laptop; loaded the software and can see the cable identified in the Device Manager; set the com port to 1 as required by the meter, but no data is transferred from the meter.
    The local computer shop says that the BIOS needs to be set up for the USB ports to be seen as COM ports, but the Dell BIOS has nothing that appears to affect this. I believe it’s a hardware problem, maybe a bad green cable. Any comments?

    • David Roberts Reply

      Thanks for posting your question. There should be no need to set up COM ports in the BIOS for USB serial. Windows does this in software. We have sometimes seen difficulties with multimeters that expected higher voltages for RS-232 than with our serial that uses the Prolific chip. The chip itself only provides TTL logic outputs, and then a serial interface chip takes those outputs and changes them to RS-232, with +7 volts for a one and -7 volts for a zero. The RS-232 standard allows up to +/-15 volts, and some multimeters appear ot require more than the +/-7 volts our chip supplies. Also, you didn’t mention if your adapter was from Plugable. We don’t supply any green cables. Some devices that claim Prolific chips actually have clones that won’t work with the latest Prolific drivers. If you have a Plugable device, please contact us at, and we can help. Thanks!

      • Paul Aeberli Reply

        Thanks for the quick reply. My local computer geek store where I borrowed the cable insists that he can get it to work for the price of the cable and a coffee. I am sure you are right, as I thought it’s a hardware (voltage) problem. I have found and ordered a USB cable for the meter but will probably let him try to get it to work for fun and a coffee!

  22. Pingback: Programando dispositivos HC08 | ssihla

  23. Dafy Reply

    I have a ch340 usb to serial adopter. It installs on com 5. When I change the port number i.e. com 1 the attached printer (zebra 2844) does not work. Any suggestions? I am on win7 32bit Home.
    Thank s in advance

    • Jordan @ Plugable Reply


      This webpage is regarding the Plugable USB to RS-232 DB9 Serial Adapter with Prolific PL2303HX chipset.

      Your serial cable uses a different chipset so the information on this page may be incorrect for your situation.

      We suggest that you contact your serial cable manufacturer directly. Thank you!

  24. Dicegirly Reply

    I want to ask about COM ports when there are multiple users on a PC.
    We use a piece of document tracking software at work which has barcode scanners attached by USB to each machine.
    The software has to be configured to look on a specific port for the scanner, which is a global setting for the PC.
    However, when someone different logs on to the PC, Windows 7 assigns a different COM port number to the scanner for that person (presumably the first available) and this does not always match the COM which has been set up in the software, so needs to be reconfigured each time. The scanners don’t usually get unplugged.

    Is there a way to fix the COM port for a specific device so it never gets changed, regardless of who is logged in?

    This would save us considerable effort if these is a way.

    • David Roberts Reply

      Thank you for your comment. Have you tried using the instructions in this blog post to manually set the COM port for the same number for each user on the computer?

      • bowo Reply


        sir how to change COM 1 to COM 3 at the port serial set up for CIMCOV5

        thanks for your helps

        • David Roberts Reply

          Thank you for asking. If you are asking how to change from COM 1 to COM 3 for the adapter, you should be able to do that with the instructions in this blog post as long as COM 3 isn’t being used by another device. If it is, try changing the port for that device first, then change the port for your USB serial adapter.
          If you are asking how to change the port in the CIMCO V5 software, you will have to check your manual or contact CIMCO. I can’t find their manual online.

  25. Dan Reply

    Hi, I am trying to use a usb to serial cable, but the default windows driver is not installed properly (Prolific_Driver). I tried a couple of times with no luck. Any help please? Can you please provide a link to download another driver? “Communications Port” Driver maybe. I’ve seen that is working well, but no luck for me to find this on the internet. Thanks!

    • David Roberts Reply

      Hi Dan, Thanks for your comment. If you are using a Plugable adapter, please contact us directly at for help with this. If it’s not a Plugable adapter, it could be that it has a counterfeit Prolific chip that won’t work with the driver.

  26. Wai Phyo Aung Reply

    hi we are not connect oliveti PR2 plus computer COM port and Oliveti machine how to do this problem thank you

    • David Roberts Reply

      There are so many variables involved in Serial connections that it is difficult to answer without more details of what you are trying to do and what is happening. If you have a Plugable USB-Serial adapter, please contact us directly at We are happy to help. If your adapter is from a different company, please contact them for support. Thank you!

  27. Rob Reply

    Hi, I have thousands of the same model devices that need to be regularly programmed via a USB Serial Port. There is never more than 1 connected at a time. The problem I am having is that each one I connect, comes up under a different (com#). Is there a way to assign a consistent (com#) that they will all come up under when plugged in? I never use any other USB Serial Port connected devices either.

    • David Roberts Reply

      Thank you for your question. Unfortunately, I don’t know of any way to reliably force Windows to always use the same COM port, but it seems that if you consistently plug the adapter into the same USB port each time, it will assign the same number.

  28. Dominic Bere Reply

    Hi, I am using a device which requires COM1. I made this change successfully some while ago but I want to understand what I did and why I did it. I just followed instructions like yours (except that on my computer it is necessary to click on ‘view’ in the Device Manager and select ‘show hidden devices’ in order to bring up Ports (COM & LPT) and a few other options) but was left wondering if I should change all my ports to COM1 so that I had choice as to where to plug in my device when using it, or whether I should leave the other ports well alone on the principle that whoever set them at whatever COM they were originally set them knew what they were doing and set them like that for a reason.

    Could you please explain in very simple language what it’s all about. When I clicked on Properties without the machine plugged in the window told me the device wasn’t plugged in, and when I plugged it in it told me the device was working properly. And yet I have lots of devices, all of which must have drivers, so why is it recognising this one machine in this way? The whole thing is a mystery to me. And why do the COM options range from 1 to 256? Who could possibly use 256 of them, when I have only to select a COM value for one of my devices and all the others have apparently no preference. And what is it about COM10 that Windows sets it at that by default?

    If it would take you too much time to explain all this to me, can you tell me where I can find a layman’s explanation, please. It has bugged me for a very long time. Thanks.

    • David Roberts Reply

      The COM port setting in Windows is an arbitrary number that points to a particular address in the computer’s memory where data that is sent back and forth over a serial connection. If that number has not already been put into use to support a serial device, Windows will let you assign it to any serial device you have currently connected to the computer, such as Plugable’s serial adapter. Since the Port number is assigned by Windows when you connect a serial port, and released when you disconnect it, there would be no advantage in setting all ports to COM1. If two ports were set to COM1 and in use at the same time, this would cause problems, because one serial device would overwrite the information from the other in memory. However, this shouldn’t happen because Windows will not let you assign a COM port to more than one device at a time.

      The COM ports are arbitrarily assigned by Windows. They are not set with any purpose, so feel free to change to any open COM port when necessary. Some serial communications software will only work with a specified COM port or only with COM1 through COM4. In those cases, you have to select an appropriate port in the Port Settings window.

      The numbers range from 1 to 256 in modern Windows versions to allow a large number of serial devices to be attached without causing problems. Modern computers have plenty of memory available, so there is no problem of setting aside enough memory to support 256 ports. The number 256 is selected because it represents the maximum number of ports that can be addressed with one byte (eight bits) of information.

      When you plug in a device known to Windows, it automatically loads the driver for it. When you unplug that device, Windows automatically unloads the driver. Devices that are similar to each other can use the same driver, and Windows just copies in into memory to be used to control a particular device on a particular COM port.

      When using USB serial devices, Windows tends to assign the same COM port number to devices plugged into the same USB port. That may be why you are frequently seeing COM10.

      I hope this helps.

      Plugable Support

      • Dominic Bere Reply

        Thank you David, it does help. But it also makes me realise just how much more there is to learn if I want to understand it fully!

  29. Solar Burrito Reply

    Why can’t I see any ports in my Device Manager for Windows 7 pro? I’ve tried everything. Making hidden types visible. Still I can not see my ports. I need to make one USB set to Com1. Any ideas?

    • David Roberts Reply

      Do you have a USB-Serial adapter attached? Unless you have a built-in serial port or a USB serial adapter, your computer won’t show normal COM ports (it might show virtual COM ports, like Bluetooth ports). If you have a serial adapter connected and it’s a Plugable one, please contact us at We can help with this. Thanks!

  30. Ben Reply


    We are using at my workplace Pinpad at dedicated COM 10. However, in some cases when someone is not using the right process the COM port is changed to another free COM port. Then we need to change it manually and to reboot the machine. is there is a way to “Close” the COM port so it will not change at all?

    • David Roberts Reply

      Windows checks the USB Vendor ID(VID), Product ID (PID) and device serial number each time a USB-Serial device is plugged in, and assigns the next unoccupied COM port if it has not seen that combination of VID, PID, and serial number before. Also, if another serial device is set to use the COM port usually assigned to the Plugable adapter, a new port will be assigned to the PLugable adapter since its previous port is no longer available. There is no setting in Windows that will prevent this behavior. If you only use one Plugable USB-Serial adapter on this computer, it is possible to set the registry so that Windows ignores the serial number of the adapter, and thereby assigns the same port to any Plugable adapter that is plugged in, but if you are using multiple Plugable adapters, this will make the situation worse. If you would like more information, please contact us directly at with some details about your setup, such as how many serial devices are connected, and how many Plugable devices are being used, and we can give more specific information.

  31. Ben Reply

    Thank you David.
    Other COM’s ports are used as well (i.e: COM 5). So I understand that it is complex thing to configure it..?

  32. mounir Reply

    I can’t find the ” port com & lpt ” in my win 7 ultimate …where I can find it ?

  33. Patience Mabasa Reply

    Hi! When I plug in a USB it automatically open. How can I change it to prompt me before opening.

    • David Roberts Reply

      Hi Patience,
      Thank you for contacting us. I’m not sure I understand the question. Could you please tell me what is automatically opening when you plug in the USB? Also, is it our USB-Serial adapter that you are plugging in?

      Thank you!

  34. Patryk Mędrek Reply

    Hi. I have win 8.1. What do I have to do to see COM ports? As I do have only USB shown under device manager… Do I need to get some special cable/ convener?

    • Pat Reply

      Hi Patryk,

      Thanks for asking! The COM port section in the device manager is only available when a Serial Port is detected on the system. This can be a built-in serial port, PCI or PCIe serial card, or a USB Serial Adapter like our Plugable PL2303-DB9 USB to DB9 RS232 Serial Adapter ( ). Without one of these physical serial ports the computer will not display the “Ports (COM or LPT)” section in the device manager.

      If you have any additional questions, please feel free to email our support team directly at “”, we are happy to help!


  35. Mitchell Reply

    Dear Bernie,

    Thank you for your article. It was very informative. I have a slightly off topic-question.

    I am writing some software that needs to know what COM ports are actually available/connected on a Windows machine i.e. it needs to know where to communicate before doing so.

    Can you suggest a means to determine this ? (Think high level stuff like ‘open file COM1:’ and return a value for success or fail). Yes, I know its odd but the language is new to me and I am unsure if I can even do BIOS calls from it.

    Any help would be appreciated.

    • Pat Reply

      Hi Mitchell,

      You’re welcome!

      For your question regarding finding the active or assigned COM ports, Windows.Devices.SerialCommunication namespace ( ) may be helpful. Unfortunately RS-232 predates plug and play technology making it difficult to determine if a port is actually connected, normally the connected device will have to respond to whatever command or data is sent for the system to determine if the port is connected. I hope this helps to get you started!

      Plugable Technology

  36. Kate Reply

    Thank you for your information and this is a useful post. But I have a problem about using 2 functions in the same USB class. I use USB CDC as WinUSB but now I want use USB CDC for both WinUSB and Virtual Com Port. Is this possible? Thank you for your time!

    • Pat Reply

      Hi Kate,

      Thanks for reaching out to us, I am happy to help!

      I am not 100% sure I follow what you are trying to do with the serial adapter, in most cases only a single application can control the serial port at a given time. Is it possible to provide any additional context or details on the setup? If you would rather not post additional details in a public forum please feel free to email our support team directly at

      Thank you,

Leave A Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.